This invention relates in general to coating substrates by vapor deposition and in particular to a new and useful arrangement for coating substrates in an apparatus for vacuum deposition in which the substrates are held on a plate having holders arranged in holes such that their axis of rotation intersects on a point along the axis of rotation of the plate and wherein a vapor beam correction screen is located adjacent the plate and rotates in an opposite direction to the plate.
A substantially highly accurate uniformity and evenness in coating of spherical or planar surfaces, for example of optical lenses, can be obtained by vacuum deposition. That is, random variations of the beam intensity of the evaporative source which may occur during the coating operation affect the layer thickness very little and correspond to a numerical value in the order of 0.1% of the layer thickness.
Much greater deviations are caused by the inaccuracy of the structure supporting the substrates. Already deviations of .+-.0.3 mm for example, from a nominal value of 600 mm of the main radius of curvature of the spherical plate produce approximately the same variations in layer thickness as random variations in the beam intensity. However, with spherical plates obtained, for example, by drawing and punching from a 3 mm Cr-Ni steel sheet, such narrow tolerances can never be observed. As a rule, the deviations exceed more than tenfold the above mentioned values. It would be very expensive to produce sherical plates of larger thickness, having a satisfactory ridigity.
There is known a prior art arrangement for uniformly coating surfaces of revolution by vapor deposition in high vacuum, comprising a substrate holding structure rotatable about an axis, an evaporative source provided near the axis of rotation and a correction screen for the vapor beam, which is mounted close to the substrate holding structure and rotates about the same axis in opposite direction. To obtain a desired high accuracy in coating, this arrangement again requires substrate supports which are sufficiently rigid.